Kyle Eastmond will finish the season with St Helens before switching codes to play for Bath. Photograph: Mike Egerton/Empics Sport

St Helens have already begun their search for a scrum-half replacement for Kyle Eastmond, whose move to rugby union with Bath has finally been confirmed, while struggling to conceal a sense of betrayal at his decision to leave.

The 21-year-old has been with the club for almost a decade, but after only 60 first-team appearances he has chosen Bath's offer of a three-year contract ahead of the new deal on the table from Saints – although as things stand he is due to stay in the Super League until the autumn.

"It is a pity, because the club has invested so much time and energy in Kyle's development," said the St Helens chairman, Eamonn McManus, pointedly. "But we've lost much bigger players than Kyle in recent years and coped OK, and we'll carry on now. We've started thinking in terms of finding a replacement – looking at the options we have from within, and seeing what's outside, both in the overseas and domestic market. It's for next season so there's no mad rush, but I don't think we're the only Super League club looking around for half-backs."

McManus hopes that Royce Simmons, the veteran Australian who is in his first season as the club's head coach, will give Saints an advantage overseas. "Royce is obviously up to speed as to who's doing what and may be available from Australia," he added.

However, with Simmons committed to a routine hospital appointment, it was his assistant, Kieron Purtill, who was left to discuss the confirmation of Eastmond's departure. "We've got to look forward now, and enjoy the time we've got left with him," said Purtill. "Kyle's a Saints player until the end of the year, and we're all professional people."

Eastmond will travel to Perpignan for Saints' game against the Catalans Dragons on Saturday, when his regular half-back partner Leon Pryce is expected to return from a groin injury suffered in pre-season. That could leave Simmons with a dilemma, as Lee Gaskell has been more impressive than Eastmond in recent matches.

"Leon is 99% to play on Saturday after doing his second full training session today, but Lee's definitely not done anything wrong in the last couple of games that would make him easy to leave out," said Purtill.

However, Simmons, the veteran Australian who is in his first season as the club's head coach, is likely to be a key figure as they look to add a couple of high-profile signings for next season not only to replace Eastmond, but to ensure that they can fill the new 18,000-capacity stadium which is currently being constructed on the site of an old glassworks.